This invention relates to a push button switch assembly and method and, more particularly, to such an assembly and method according to which a membrane switch is manually actuated.
Many forms of push button switches are in the prior art, and several involve manual actuation of a membrane switch. These latter designs includes an opposing pair of flexible electrodes separated by a dielectric layer. A plurality of integral outwardly-extending protrusions are screen printed on the exterior surface of each electrode, one over each of the opposing contact portions to concentrate an applied force to bring the respective electrode contact portions together into electrical contact. This assembly will hereinafter be referred to as the "membrane", and the switch is activated, or closed, by pushing on a selected area of the membrane.
Some push button switches of the above type include an enlarged pivotal button which is manually pushed towards the membrane to activate the switch. An enlargement, or bumper, is provided on the back side of the button and is often provided with a domed, or rounded, end for engaging the membrane. In this manner, the button provides a relatively large contact area for manual engagement, while the bumper engages the relatively small, critical area of the membrane that activates the switch.
However, there are problems associated with this type of assembly. For example, the button and the associated bumper are usually fabricated integrally of hard plastic. Therefore, when a relatively large force, such as 40-50 pounds, is applied to the button, and the force is transmitted by the bumper to the membrane, it can damage the membrane.
Another problem with this type of switch occurs when the switch is located in an outdoor environment, such as a gasoline dispensing station located at a service station, and is therefore subjected to relatively low temperatures. In these environments, even if the bumper is fabricated of a soft material, such as an elastomer, to avoid the transmission of excessive forces as discussed above, this material will be subjected to a compression set at relatively low temperatures. As a result, after a few cycles of use, the bumper will not reach the membrane, or at least will not reach it with sufficient force to actuate the switch.
Therefore, what is needed is a switching assembly of the above type which does not damage the membrane when relatively high forces are applied to the button, and is operable at relatively low temperatures.